The invention relates to a process for producing burr-free workpieces by blanking, in particular in a counterblanking tool, a blanking strip from which the workpiece is to be blanked being clamped between an upper and a lower blanking die and an upper and lower punch and blanking being effected by cooperation of an upper and a lower punch.
The blanking discussed here is a modification of a blanking procedure. Whereas, in blanking, a blanking strip is acted upon by a punch on one side, in fine blanking the blanking strip is clamped between a blanking die and a press plate, a punch and a pressure pad.
The quality of the cut surface of the workpiece is thereby considerably improved.
So-called fine counterblanking or fine counterstamping is furthermore also known, in which the blanking strip is clamped between two blanking dies and two punches. According to this method, a punch makes an initial cut in the workpiece counter to the pressure of the other punch, the pressure of this cutting punch exceeding that of the other punch.
After the initial cutting, there is a reversal of the pressure build-up, i.e. the pressure on the other punch exceeds the pressure which acted on the first punch which effected the initial cut. As a result, an initial cut is made in the workpiece from the other side.
Subsequently, there is then once more a reversal of the pressure build-up, i.e. the pressure of the first punch exceeds the pressure of the other punch, the workpiece thereby finally being blanked out.
A process of this kind is described, for example, in German Patent 2,727,445. A disadvantage of this process is that a separate workstation has to be provided for each operation in the fine blanking device and this makes the overall procedure slower and more expensive.
Furthermore, it has proven particularly disadvantageous that, as a result of the repeated pressure reversal, the device or elements of the device have to be stopped and their motion reversed. This means not only a considerable expenditure of energy but also the development of a special device suited specifically to fine counterblanking. In addition, the overall procedure is made slower.
The inventor has set himself the object of eliminating these disadvantages of the known fine counterblanking or counterstamping procedure and of developing a process which can be used in an already existing fine blanking press and, in particular, avoids a reversal of motion within this fine blanking press during a working stroke.